(1) Field of the Invention
The present invention relates to a dust protective pellicle film for use in preventing adhesion of foreign substances such as dust to a photomask, a reticule or the like used at the photolithographic step in the production of a semiconductor element such as IC or LSI (hereinafter referred to as "mask or the like"), a process for the preparation of this pellicle film, and a dust protective member.
(2) Description of the Related Art
At the photolithographic step, a mask or the like comprising a circuit pattern composed of a vacuum deposition film of chromium, formed on the surface of a glass sheet, is used and an operation of transferring this circuit pattern onto a resist-coated silicon wafer is carried out. If at this step the light exposure is performed in a state where a foreign substance such as dust adheres to a circuit pattern on the mask or the like, also the foreign substance is transferred on the wafer and a defective product is formed. Especially, when the light exposure is effected by a stepper, the risk that all of chips formed on the wafer will become defective increases. Accordingly, adhesion of a foreign substance to a circuit pattern of a mask or the like is a serious problem. As the means for coping with this problem, there has recently been proposed a dust protective member (pellicle) comprising transparent light-transmitting dust protective films (pellicle films) arranged at appropriate intervals on one or both of surfaces of a mask substrate of a mask or the like.
Generally, this dust protective member comprises a holding frame composed of aluminum and a transparent light-transmitting dust protective film of an organic substance such as nitrocellulose spread on one side face of the holding frame, and a double-adhesive tape is bonded to the other side face of the holding frame so that the dust protective member can be attached onto a mask substrate of a mask or the like. Intrusion of a foreign substance from the outside can be prevented by this dust protective member, and even if a foreign substance adheres to the film, the foreign substance is not transferred onto the wafer, and the yield is increased at the production of semiconductor elements.
With recent increase of the integration degree in a semiconductor elements, rays for the light exposure have been shifted to the short wavelength side, from g rays (436 nm) to i rays (365 nm) and further to excimer laser rays (248 nm). In the conventional light-transmitting dust protective film composed solely of an organic substance such as nitrocellulose, the bonding state of molecules is weak and photodisintegration is caused in the film, with the result that the film per se becomes opaque and the mechanical strength of the film is degraded. Therefore, the conventional film cannot be used practically satisfactorily.
As the means for overcoming this problem, there has been proposed a light transmitting dust protective film composed of an inorganic substance, such as synthetic silica glass, fused silica glass fluorite, in which the bonding of molecules is strong and photodisintegration is hardly caused (see Japanese Unexamined Patent Publication No. 62-288842 and Japanese Unexamined Patent Publication No. 63-6553). In the case where a film is formed from an inorganic substance as mentioned above, since the film has no pliability, formation of a single layer film is difficult, as compared with the case where the film is formed from an organic substance.